Portable communicators, particularly cell phones, sometimes use multiple radiators so that one radiator is active in a retracted position and the other is active in an extended position. Retraction of the antenna allows a user of the phone to store it in purses, briefcases, and more recently, even in shirt pockets. Having an active antenna in the retracted position permits use of the phone, such as stand-by operation, with the antenna in the retracted position. In areas where reception is poor, the antenna might be extended to avoid interference, for example, resulting from the head of a human user. The blocking effect of a human head can adversely affect the low power signal between a base station and a cell phone, thereby reducing the quality of communications.
An additional use of separate radiators in an antenna is to enable phones to receive two different types of signals. These phones are compatible then with multiple cellular networks. Thus, for example, an antenna might act as a half-wave radiator in an extended position, and as a quarter wave radiator in a retracted position. Conventional solutions to providing such radiator antennas frequently utilize a capacitive coupling. These provide lower quality than galvanic couplings. In addition, a complicated switching arrangement is often required to disable the capacitive coupling.
An additional problem concerns antennas having an exposed electrical contact at an end for contact to phone circuits. As the antenna is retracted or extended, the electrical contact sometimes catches or contacts circuits or phone portions in an unintended and undesirable manner.
In sum, a dual radiator antenna should provide efficient operation in its separate retracted and extended positions and should avoid complicated structures and switching requirements. In addition to these specific desirable qualities, the performance of the antenna should be robust and should not significantly degrade from a small number of cycles of retraction and extension during use. There is therefore a need for an improved antenna which exhibits such qualities.